The Opelousas courier., 1887-04-16
MECHANICAL.

SOME blulS dBO OAESIluISAGo WStS
made to ascertain the proportion OF
oxygen in the river Thames at low
water, it being found that as it run
through London, the quantity of oxy-
gen diminishes as compared with the
proportion it contains at Richmond,
about twelve or thirteen tons of oxygen
being lost between Richmond Bridge
and Somerset House. Recent tests of
the Thames water show that near the
sewage soutfall it contains but about
half a cubic inch Of oxygen per gallon,
instead of two cubic inches per gallon,
as above the city; but lower down the
proportion of oxygen rises again until
the water is within ten per cent. of its
richness in oxygen at Richmond. Thus
the considerable power which flowing
water possesses of keeping itself sweet
and clean is regarded as positively
proved, though the power, great a it
is, may be and often is oyertaxed when
the organic matter is non-living. As
to whether it has the power of destroy
ing those minute living organisms
which are the germs of certain dis
eases, different opinions exist among
scientists.
The quality of a good slate is that
it should cleave readily, that the lam
ine should be straight and unmixed
with foreign substances, and the more
finely laminated it is the larger plates
will be obtained. Slate for roofs should
be dense and not porous, and it is best
judged, like other %stoses, by the sharp
ness of the sound. Porous plates are
bad, because they swallow water. Sui
phur is a dangerous ingredient, and
sometimes exists in particles so minute
as to be i~mperceptible. This mineral
when mixed with water produces Wit
riolic acid, and so promotes decompo-
sition. To detect its presence heat the
slate with wood embers, and if it exists
it will give forth a sulphurous smell.
Oxide of iron mixed with slate has ?
sympathy for air and water, and so in
creases the quantity of oxide or rust.
Calcareous matter is equally injurious,
and may be tested by observing wheth-
er it puffs up when exposed to muriatic
acid. Carbonaceous or coaly matter
may be detected by burning. With re-
gard to it's color, yellow or black spots
indicate the presence of. oxide, and
black that of carbonaceous matter
Mechanical World.
VICE PRESIDENT CHANUL, in his ad
dress before the mechanical section OF
the American Association, considered
what might DE called the evolution OF
inventions. Nothing, he said, is more
remarkable than the multitude OF minds
and facts which are required for the
perfecting of even a simple machine,
or how little the last man may need to
add to complete the invention. Facts
and natural laws. known for years a,
curiosities. are taken up by some in.
ventor, who fails in the attempt to
render them of practical use; then a
second genius takes hold, and profit
ing by the piistakes of the first, pro,
duces at great cost a working machine.
Then comes the successful man, who
works out the final practical design,
and, whether making or losing a for
tune, yet permanently benefits man.
kind. This course is exemplifed in
the address by the relation of the
growth of the steam engine; and 81
with other inventions. Tie, steamboat
was being developed from 17C0 to 1907;
the locomotive from 1902 to 1929; the
telegraph from 1929 to 1874; the sew.
ing machine, with its 1900 patents,
from 1880 to 1860, and the reaping
machine for seyenty-fiye years, the last
successful man adding bit little to the
work of his forerunners. The rule has
been that "the basis of success lay in q
thorough acquaintance with what had
been done before, aud in setting about
improvement in a thoroughly scientific
way."-Popular Science Monthly.